A sticker, a marble and a bead costs $7.80 altogether.
The sticker costs $1.10 less than the marble.
The bead costs $1.40 more than the marble.
How much do 5 beads cost?
Choose the cheapest item to be 1 u.
The sticker costs $1.10 less than the marble.
The cheapest item is the sticker.

Cost of the sticker = 1 u
Cost of the marble = 1 u + 1.10
Cost of the bead = 1 u + 1.10 + 1.40 = 1 u + 2.50

Total cost of the sticker, the marble and the bead
= 1 u + 1 u + 1.10 + 1 u + 2.50
= 1 u + 1 u + 1 u + 1.10 + 2.50
= 3 u + 3.6

3 u + 3.60 = 7.80
3 u = 7.80 - 3.60
3 u = 4.20

1 u = 4.20 ÷ 3 = 1.40

Cost of 5 beads
= 5 x (1 u + 2.50)
= 5 x (1.40 + 2.50)
= 5 x 3.90
= $19.50

Answer(s): $19.50